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A171652
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The initial decimal digits of 2^a(n) are the decimal digits of n followed by n.
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2
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50, 51, 25, 145, 142, 119, 86, 239, 93, 1558, 1598, 761, 1183, 6651, 5515, 4183, 34, 8990, 1343, 4180, 7987, 10628, 938, 5519, 4177, 10213, 10326, 6652, 1327, 5516, 12326, 4184, 11964, 6928, 6649, 8991, 653, 10373, 11549, 4181, 3706, 7988, 5862, 10629, 8988, 939, 13084
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history;
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OFFSET
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1,1
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REFERENCES
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E.I. Ignatjew, Mathematische Spielereien, Urania Verlag Leipzig-Jena-Berlin, 2. Auflage 1982
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LINKS
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Table of n, a(n) for n=1..47.
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EXAMPLE
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a(1) = 50; 2^50 = 1125899906842624
a(2) = 51; 2^51 = 2251799813685248
a(3) = 25; 2^25 = 33554432
a(10) = 1558; 2^1558 = 10109583053...744
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PROG
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(PARI) double(n, k)=n\=10^(#Str(n)-2*k); if(n%10^k==n\=10^k, n)
a(n)=my(s=#Str(n)); for(k=1, 1e6, if(double(1<<k, s)==n, return(k)))
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CROSSREFS
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Cf. A018802, A171132, A171242, A171489, A171617
Sequence in context: A207142 A207141 A165871 * A078289 A043618 A134691
Adjacent sequences: A171649 A171650 A171651 * A171653 A171654 A171655
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KEYWORD
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nonn,base
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AUTHOR
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Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Dec 14 2009
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EXTENSIONS
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More terms, program, and editing by Charles R Greathouse IV, Aug 02 2010
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STATUS
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approved
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